The effect of mechanical polishing on hydrogen permeation in iron single crystal

Abstract

The permeation of hydrogen through a metal such as iron or steel which contains saturable traps has been analyzed in several ways. Using an arrangement of specimen and electrolyte one can measure the time of transit of the hydrogen through the specimen after charging began. This is the ''break-through time.'' It is known that the apparent hydrogen diffusivity is reduced by structural defects such as a dislocation, a microvoid, a grain-boundary, and an interface of nonmetallic inclusions, etc.. Changes of dislocation density in the surface layer were monitored b, positron annihilation. Agreement between hydrogen traps and positron traps was established. Using positron annihilation, they have shown that the effect of mechanically polishing a single crystal of iron is to produce a layer about 25 ..mu..m thick which contains dislocation traps. The purpose of this investigation is to assess the effect of a thin layer of such traps on the diffusion of hydrogen through the specimens which are several hundred ..mu..m thick, and to determine the trap concentration profile in the sub-surface layers of and to determine the trap concentration profile in the sub-surface layers of it.